9210 & XPERT DATALOGGERS MODBUS Manual - Sutron ...

SUPPORTED MODBUS FEATURES
This section discusses what portion of the MODBUS standard are supported by the modbus.sll
library. To compare the features implemented by this library versus standard MODBUS, it may
be helpful to refer to http://www.modbus.org for more information.
Data Link Layer
This library supports MODBUS messaging over asynchronous serial transmission, e.g.,
EIA/TIA-232 or EIA/TIA-485 in a master-slave arrangement, as well as over TCP/IP. Xpert can
be either a MODBUS master or slave, depending on how the Xpert is configured. The Xpert can
be both a master and slave on separate ports.
MODBUS communication over radios is supported through use of the hardware control lines.
The user can specify delay and wake-up parameters to facilitate this mode of communication.
RDI radios can be used for MODBUS messaging when this library is used in combination with
RDI.sll, available separately.
MODBUS communication over modems is supported as long as the modem is manually
configured prior to use. The modem must be configured for auto-answer, disabled hardware flow
control, and DCE to DTE baud rate. Set the parity setting in the MODBUS configuration to
“None”.
The following commands will configure the Sutron Voice Modem for MODBUS
communication. Send these commands to the modem using a terminal program like HyperTerm
set for 19200 baud. Then connect the modem to the Xpert.
Command Description
AT&F Reset modem to factory defaults.
ATS0=1 Set modem to auto-answer on 1 ring.
AT&K0 Disable DTE-DCE hardware flow control.
AT+IPR=19200 Set DCE to DTE baud rate to 19200.
AT&W Write new settings to default configuration.
To verify the settings have been properly set, you can tytpe AT&V to view the settings for the
active and stored profiles.
Application Layer
This section describes the application-layer standards that are supported by Xpert‟s modbus.sll.
Message Format
The MODBUS serial communications standard specifies two different message formats, or
modes, named RTU and ASCII.
The RTU message format represents data using a standard big-endian binary format.
The ASCII message format represents data using 2 ASCII characters to describe each binary byte
in terms of its ASCII hexadecimal representation (e.g., the value 0xC9 would be communicated
by sending the ASCII characters „C‟ and „9‟, as opposed to sending a byte having the value
0xC9, as would occur in RTU format).
The Xpert modbus.sll library supports RTU, ASCII, and TCP/IP message formats.
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